#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>

#define BUF_SIZE 100
void error_handling( char *buf);


int main( int argc, char *argv[])
{
    int serv_sock;
    int clnt_sock;
    struct sockaddr_in serv_adr;
    struct sockaddr_in clnt_adr;
    struct timeval timeout;
    fd_set reads;
    fd_set cpy_reads;

    socklen_t adr_sz;

    int fd_max;
    int str_len;
    int fd_num;
    int i;

    char buf[BUF_SIZE];

    if ( 2 != argc ) {
        printf("Usage : %s <port> \n", argv[0]);
        exit(1);
    }

    serv_sock = socket( PF_INET, SOCK_STREAM, 0);
    memset( &serv_adr, 0, sizeof( serv_adr));

    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = htonl( INADDR_ANY);
    serv_adr.sin_port = htons( atoi(argv[1]));

    if ( bind(serv_sock, (struct sockaddr *) &serv_adr, sizeof(serv_adr)) == -1)
        error_handling("bind() error");
    if (listen(serv_sock, 5) == -1)
        error_handling(" listen() error");
    
    FD_ZERO( &reads);
    FD_SET( serv_sock, &reads);
    fd_max = serv_sock;

    while (1)
    {
        cpy_reads = reads;
        timeout.tv_sec = 5;
        timeout.tv_usec = 5000;

        if ((fd_num = select(fd_max + 1, 
                             &cpy_reads, 
                             0, 
                             0, 
                             &timeout)) == -1) {
            break;
        }

        if (0 == fd_num) {
            continue;
        }

        for ( i = 0; i < fd_max + 1; i++)
        {
            if ( FD_ISSET(i, &cpy_reads)){
                if ( i == serv_sock){
                    adr_sz = sizeof( clnt_adr );
                    clnt_sock = accept(serv_sock, (struct sockaddr*) &clnt_adr, &adr_sz);
                    FD_SET( clnt_sock, &reads);
                    if ( fd_max < clnt_sock) {
                        fd_max = clnt_sock;
                    }
                    printf(" connected client: %d \n", clnt_sock);
                }
                else {
                    str_len = read( i, buf, BUF_SIZE);
                    if (0 == str_len) {
                        FD_CLR( i, &reads);
                        close(i);
                        printf("closed client: %d \n", i);
                    }
                    else {
                        write( i, buf, str_len);
                    }
                }
            }
                
        }
        
    }

    close( serv_sock );


    return 0;
}


void error_handling( char *buf)
{
    fputs( buf, stderr );
    fputc( '\n', stderr );
    exit( 1 );
}
